Signaling system



May 14, 1940. N. M. RUST SIGNALING SVYSTEM Filed May 5, 1936 Trans/n if fer Repeafer Aepea fer Repea' ref f/l'gh pass f/her Receiver Low pass fi/fer INVENTOR Noel Meyer R052 ATTORNEY Patented May 14, 1940 V UNITED STATES ATENT OFFICE SIGNALING SYSTEM Noel Meyer Rust, Chelmsford, to Radio Corporation of America,

, of Delaware England, assignor a corporation In Great Britain, May 11,1935

1 Claim.

This invention relates to electrical energy transmission systems and more particularly to cable systems for transmitting television and like signals.

Serious difficulties arise in seekingto transmit television signals over cable lines, these difficulties being due to the very wide range of frequencies involved, the said range extending in many modern high definition systems from 25 cycles per second, or even lower, to 2 megacycles or higher. It is in practice so expensive as to be commercially impracticable to design and manufacture long cables which will introduce constant time delay over such a very wide range of frequencies extending down to 25 cycles per second, or lower.

According to this invention, television or like signals are transmitted over cables designed to give substantially constant time delay for all the signal frequencies above approximately the scanning line frequency, and at the receiver end the lower frequencies below the minimum frequency over which the cable transmission systern gives constant time delay, and in particular the framing frequency and near-frequencies, are separated out, subjected to a time delay corresponding to one or more picture frame periods and are then combined with the higher frequency signals, and fed to the receiver proper.

The invention may becarried into practice with cable systems consisting of relatively cheap small co-axial conductorhigh frequency cables of the air spaced type, and such cables when used in systems having repeaters every 20 kilometres. or

so, may be designed to give practically constant time delay over all television signal frequencies above about 6 kilocycles (in television systems wherein twenty five 250 line pictures are transmitted per second, the scanning line frequency The invention is illustrated in the accompanyin drawing which shows in block diagram form one way of carrying outthe invention.

Referring to the drawing, i represents a television transmitting station (operating for exam.-

ple, with twenty five 250 line pictures per second) from which all the television signals from the framing frequency (25 cycles per second) upward are transmitted over a high frequency cable transmission system such as that above described and equipped with cables 5 with in serted repeaters 3 having the usual amplitude correcting arrangements every 20 kilometres or thereabouts, and at the receiving end of the cable system the channel is branched out into two branches 1, 9, the branch 1 accepting the applying amplitude correction to all signals of a frequency equal to or above the scanning line frequency (6250 cycles per second in the present example) but rejecting all frequencies below the said scanning line frequency. This may, for example, be: a high pass filter. Suppose the whole transmission system up to the output terminals of the branch! imposes a constant time delay t1 upon all frequencies equal to, or above, the scanning line. frequency; then the other branch 9 is arranged to faccept the low frequencies (the framing frequency and what may be termed the floating zero frequencies which define the general level of illumination) to impart thereto a constant time delay equal to tl-i-np where n is a whole number, and p is the number of pictures or frames per second. ciated that it may be, for example, a low pass filter. I a l V The outputs fromthe two branches are combined and fed at II to a television receiver or, if the signals are to bentransmitted further, to a television signal rediffuser. Thus, in the system now described where twenty five 250 line pictures are transmitted per second, the branch 1 could be arranged to pass the band 6250-1, 500,000 cycles per second and the branch ii to pass a band 10-50 cycles per second. If desired, the upper limit of the band passed by the branch 9 may be extended above about 50 cycles so as to pass also one or more of the harmonics of the picture repetition or framing synchronizing frequency. This will facilitate the obtaining of sharp and accurate synchronization by passing the harmonics necessary 'tothe obtaining of sharp pulse formation. It will be readily appreciated that in order to maintain correct phasing of the various components of the signaling current, phase correcting networks of the type well known in the art may be inserted before the repeators or suitable phase correcting networks may be connected in series with the high pass and/or low pass filters. Apparatus suitable for performing the requisite functions at I, 3, l, 9, and I I is well known per se to those skilled in the art and it is, therefore, unnecessary to describe it herein. For example, the transmitter may be of the type disclosed in the Smith Patent No. 2,132,655, issued October 11, 1938 and entitled System for producing electrical impulses while the repeaters may be of the type shown in Smith Patent No. 2,045,315 which issued June 23, 1936, for Amplifiers. The filters 1 and 9 may be any one of the type described in the book entitled It will be appre-w Transmission Networks and Wave Filters by Shea, Van Nostrand Co. (1929) New York City, while the receiver may take the form shown by the Osbon Patent No. 1,934,321 issued November 7, 1933 for Cathode ray oscilloscopes. It will be seen that in the system as just described television signals between about 50 cycles and 6250 cycles per second, will be lost so far as the receiver is concerned but in practice this loss is not serious The extent to which signal frequencies may be permitted to be lost in this manner is a'matter of degree, and it will be appreciated that the invention provides a compromise between the divergent requirements of utilizing fully all the picture signals and satisfactorily transmitting television signals over a reasonably economical transmission line system.

Having now described my invention what'I claim is:

An electrical energy transmission system for television signals comprising a cable transmission system adapted to give a substantially constant time delay 151, for all-the television signal frequencies above approximately a predetermined frequency, an output and input, end for said system, segregating means at the output end of said system for separating outtelevision signal frequencies including a second predetermined frequency 10, means for imposing a time delay '"tH-np (where n is a whole number) upon said separated frequencies, and means for combining the separated, delayed, low frequencies with the frequencies above that for which said cable system imposes substantially constant time delay to produce substantially constant time delay for the picturesignal frequencies above and below the predetermined frequency.

NOEL MEYER RUST. 

